His study looks very much like home - every surface carefully piled with books, files, photos and manuscripts - but it is not where Ryszard Kapuscinski really lives. The attic room in his reconstructed prewar house in central Warsaw is the place he comes back to, every now and again, to reflect on an extraordinary journey just ended and to plan the one about to begin. Over the past five decades, these quests have taken him to every forgotten extremity on earth. He has returned here to recuperate, or to escape the firing line, or simply to get out of the sun. Pinned onto the beams of the attic are a lifetime of poems, quotes and aphorisms, scraps of itinerant wisdom. Among them is a headline ripped from a newspaper: 'World is very big trouble.'

For Kapuscinski, much of this big trouble - most of the 27 revolutions he's witnessed first hand - has occurred in Africa, where for the Sixties and Seventies he was Poland's only foreign correspondent. Africa is the leading character of Kapuscinski's most extraordinary work, including The Emperor, one of the past century's handful of indelible books, an account of the imperial court of Haile Selassie, part comedy of manners, part anatomy of a tragic megalomania, and The Shah of Shahs, his surrealist account of the fall of the Pahlavi dynasty and the fundamentalist revolution in Iran.

It is the place, too, where he had his youth and where he came of age. His new volume, The Shadow of the Sun, is perhaps the closest this most essential of the world's writers, now nearly 70, will come to an autobiography. And, appropriately, it is also a memoir of a continent, told as a series of remarkable episodic adventures.

When he first arrived in Accra in 1958, Kapuscinski was perhaps uniquely qualified to tell the story of that 'other planet'. As a boy, he first smelt Africa in Mr Kanzman's little shop, Colonial and Other Goods, purveyor of almonds, cloves and cocoa, in his home town of Pinsk, now part of Belarus, what he describes to me as 'the poorest, most afflicted, most miserable part of Europe'. To illustrate his point, he gets a book down from one of his steepling shelves, a collection of misty photographs of the lost world of his childhood - thatched huts, carts drawn by oxen, floating markets, marshy jungle; no gaslight, no electricity, no roads. 'So it was always like being in the villages of the Congo,' he says, smiling a little. He was the son of the local schoolteacher and his dreams were African dreams, too, of shoes and of food.

In 1939, Kapuscinski's father was taken prisoner of war by the Russians, but he escaped from the camp before he was deported to Siberia. The family smuggled themselves across the shifting Polish border in a horsedrawn cart and fetched up on the blasted outskirts of Warsaw. During the Nazi occupation, his father continued to try to teach, while working for the underground. After the war, again under Soviet rule, at a secondary school with no windows and bombed-out walls, there was only one book which the boys in Kapuscinski's class would pass around to learn to read, a copy of Stalin's The Problems of Leninism.

Kapuscinski wrote poems, had a young man's ambition to see the world, but his imagination, at that time, stretched no further than neighbouring Czechoslovakia. The day he left school, because he could write, and because a whole generation of Polish intelligentsia had been killed or deported, Kapuscinski was hired by a Warsaw newspaper. In the years that followed, he made a name with investigative reports critical of the 'advances' made by the Soviet regime, and eventually his editor decided to send him abroad, partly because he had a grasp of English, partly, you guess - ironically - to keep him out of harm's way.

He went first to India aged 24. 'I felt overwhelmed by it,' he says remembering, eyes shining. 'But when I arrived, I did not understand even when people were talking to me in English. And I started to cry, did not know what I would do, how I would work. I was walking down the street and there was a man selling books on the street, and I bought two: an old Penguin edition of Hemingway's For Whom the Bell Tolls and a small dictionary. And I went to my old hotel in Old Delhi and I opened the novel and I opened the dictionary and I started to go through it word by word, and slowly I learnt.'

Presumably, I suggest, there was a great sense of liberation just to get out of Warsaw.

'Yes, of course,' he says, 'but I was not thinking of that. I was thinking all the time of the enormous task in front of me. You have to understand I had no idea at all of the world, no history, no sense of culture. And I realised I have to learn and learn and learn. And I am still continuing with this. The world is so big and it is so difficult to describe it.'

Kapuscinski made it his business to travel more in hope than expectation; his stories often begin with sentences like this one: 'I arrived in Kumasi with no particular goal.' He kept his mind open to chance - his face is animated by the possibilities of life - and where he could, he kept away from the pack of other journalists: 'I always thought,' he says, 'that if you go on assignment you should always go alone. If you go even with one other person, that person influences your perception of what is out there. It is better, necessary, to face these other realities alone, and to see how you respond to them without any interference and be responsible to that.'

When Africans looked at him, he knew exactly what they saw: 'The white man, the one who took everything from me, who beat my grandfather on his back, who raped my mother slavery, colonialism, 500 years of injustice'

But Kapuscinski refused to be guilty for the sins of other men's fathers. Instead, he told villagers that he, too, as a Pole, was the victim of terrible colonial oppression, had known what it was like to live in constant hunger, but when he did so they smiled incredulously and walked away. Still, he refused to let it rest. And to prove his point, his humanity, he went to live among the people he wrote about - in a lean-to room in the desperate shanty towns of Lagos, sharing a handful of rice with the starving subsistence farmers of the Sahel - and tried to tell the stories of their emerging countries as they might have told them.

He arrived at a propitious moment. Kapuscinski's Africa began in 1958 in Ghana and in hope, listening to the revolutionary words of Kwame Nkrumah, the first in a long line of independence leaders whose careers he saw begin in electric optimism and often end in infamy or despair or violent death. In one year alone, 1960, 17 African countries ceased being colonies, and Kapuscinski was there to record it all.

'But at the same time, I was very busy,' he says. 'I knew that what I was doing was very superficial. The way in which Africa was often reported: "President of Togo went to visit President of the Ivory Coast". It's totally meaningless, and even as I was doing that, I knew it.' So as well as sending news of 50 countries back home on the wire Kapuscinski began compiling another kind of intimate account of Africa in his head. 'Each of my books,' he says, 'I see as a second volume. The first volume of events was news items. But the books I did for myself. To try to understand these things for myself.' Into them he poured everything he knew. 'I was very interested in anthropology and oral history and I was reading everything, fiction, travel, history, science, poetry and trying to use all that I was reading.'

In this way, over the years, Kapuscinski has created his own kind of reporting and he has come up with many ways of describing it. Sometimes he resorts to the Latin phrase silva rerum - 'the forest of things'; at other times, he calls it 'literature by foot'; whatever it is, it is much more than journalism, more an old-fashioned storytelling given a modernist edge of dislocation and irony. 'I witnessed in effect history in the making, real history, our history,' he says. 'But I was also surprised. I never saw another writer in Africa. I never met a poet or a philosopher or even a sociologist then I would return to Europe and I would find them, writers writing their little domestic stories: the boy, the girl, the marriage, the divorce.'

Back home in Poland, his accounts of the vanity and corruptibility of power, and the comic, terrifying structures of dictatorship were read as dissident parables of the mutability of the Soviet-backed regime. Such parallels were accidental, Kapuscinski says, his eyes quick with mischief, but still impossible to ignore. He became involved in establishing the Solidarity movement at home in the early Eighties, but his real political work was done thousands of miles away, often at great personal risk.

Where I wonder, does he think his restless sense of vocation came from?

Kapuscinski passes his hands over his face, shakes his head a little, as if at the troubles he's seen. 'I don't know where it came from: my father? My childhood? Or simply from seeing these people who have nothing to expect from life. But mostly I think I understood that to know anything at all about these cultures - in Rwanda, say, or Ethiopia - and to have the gift of describing them - you have to have a bit of the zeal, the humility, the craziness of the missionary. If you are staying in the Hilton or Sheraton you will never know, you will never write these things.'

As a result of this zeal, Kapuscinski has suffered over the years, as he says, 'all types of tropical disease except Aids'. In the current book, he recounts the story of contracting cerebral malaria in the bush in Uganda, later complicated by TB. (When he awoke after one bout of hallucinatory sweating, the first face he saw staring at him was that of Idi Amin, on a hospital visit.) 'My tropical experience tells me only one thing,' he says. 'Do not eat anything that has been cut with a knife. The edge of a knife carries all the bacteria. Bananas OK; oranges OK.' Other than that, he trusts to luck.

Were there times when he thought why am I here? Is it worth it?

'Yes and no. I always went of my own free will and for my own curiosity. But sometimes in a war situation you can get in but you can't get out. Then you wonder. But that is the life, that is the choice. I know no other life and I love this life.'

Paradoxically, he says, the worst situations were never 'shooting situations', when he has been on the front line of guerrilla conflicts. The real fear occurs 'when you are sick and dying and it is hot and hopeless and there is no hope of getting to a hospital. Often you are in places where if something happens to you, no one will ever know. And you are surrounded by people who have no thoughts of self-preservation, let alone any thoughts for you. How do you appeal to these desperate people for help or assistance? The question of life and death in our culture is very important. But there are places that those questions are not so important.These are not good places to get sick. I never met a man who is not afraid in such a place.'

Has it been possible to construct any kind of normal life at home over these years?

'No. Home is where my books are.'

But it is also where his wife, and his daughter, now 48, are. Did they never say: 'Enough'? 'Never,' he says, gratefully. 'My wife has always known how important this is to me. And that this is a life that you cannot plan. I have been to places where in the whole country there is one plane and that plane may be broken. So your life becomes a matter of accident, a terrible waste of time. And in the time you are waiting for this lorry or that bus - days, weeks - all you can do is become like a stone. You have to completely disconnect. You have to learn not to worry, not to be anxious. And there are not many people prepared to do this, to waste all this time.'

He looks around his room, at the lost time contained in the typescript for his next book, about life among the Indians of the Andes, stacked on his writing table; the 'wasted' years in Africa represented by countless notebooks and fragmentary mementos, a Masai woman's decorative leather bra, an ancient rum bottle found in the Niger Delta, once the price of a slave. And then he looks back at me. 'But I believe, too, perhaps that this is the way you get to the truth of this world.'

The Shadow of the Sun will be published by Allen Lane The Penguin Press on 7 June, £18.99